Knowledge of cochlear physiology has been developed from the standpoint of electrophysiology presented by Davis' battery theory and that of cochlear mechanics originating from Békésy's travelling wave. Cochlea is an excellent acoustic equipment with a dynamic range of over 100dB and frequency range of up to 100kHz. Cochlea functions as a mechano-electrical transducer from sound to neural signals, frequency analyzer and amplifier, so-called active processes. Sound is composed of amplitude, frequency, and phase. Cochlea delivers the three sound components by a number of spikes, tonotopical information, the phase of spike of auditory neuron under 2kHz sound and an alteration of envelope from moment to moment above midrange. Details concerning these functions and the pathophysiology of hearing impairment of inner ear origin are reviewed.
Early detection of hearing loss and rehabilitation is important because hearing impairment in childhood can strongly influence language development. With the spread of newborn hearing screening, early support for children with hearing impairment has become important, however, we also experience inadequacies during follow-up.
We report the current status of children with hearing impairments and improvements. The need exists to cope with the delay in the detection of children with hearing impairments and to provide psychological support to the families after newborn screening.
Cooperation among medical facilities, educational institutions and the government, under the leadership of otolaryngologists, is desirable.
We propose improvements in the follow-up program for hearing-impaired children after newborn hearing screening (NHS) through reporting two special cases. In the first case, the subject was a girl and her mother had depression. In the second case, the subject was a boy with very low birth weight and multiple disabilities, including hearing impairment and developmental glaucoma.
These cases underscore the potential importance of the following improvements for systematic follow-up after NHS.
1)Mothers with depression tend to have difficulty in maintaining good relationships with their children. This is also the case for children with multiple disabilities. Continuous support starting before NHS to mothers with mental illness is needed.
2)Fathers' participation is important during pre-linguistic training and promotes language development in hearing-impaired children.
3)Staff members of NHS should recognize the necessity of the above and try to provide appropriate counseling to families with children diagnosed as having hearing loss (screened children).
4)Cooperation among NHS staff members and patient associations is important. Provision of feedback to regional administrations also seems to be necessary.
The present study was conducted to identify and discuss the problems related to treatment and education provided for infants with hearing loss living in Yamaguchi Prefecture, in order to improve the system. The subjects were 25 infants whose parents had consulted the Department of Otorhinolaryngology of Yamaguchi University Hospital between June 1998 and December 2012 and fulfilled the following conduction criteria: hearing loss was identified when they were under 1 year old, and information on the courses of treatment and education was available.
A review of the medical records was conducted to determine the original reasons for suspecting hearing loss and conducting the hearing tests at the age at which the infant underwent a thorough examination for the first time, the age at which the infant started using a hearing aid, and the period of treatment and education for the heaing loss.
As one of the problems identified in relation to the provision of treatment and education, since the number of institutions that provide children with these services is limited, there were infants who were unable to receive these services unless they attended institutions far from their homes.
In the future, it will be necessary to improve the system to implement treatment and education at the community level.
We examined the entry age data of hearing-impaired children who had been educated in the Fujimidai Auditory Center in Nerima District, Tokyo. The children were born between the start of the academic year of 1980 and that of 2013. Data analysis showed that 24 (10.9%) of the 220 children born between 1980 and 1999, and 91 (52.9%) of the 172 children born between 2000 and 2013 were enrolled in our educational program before they had reached one year of age. Although none of the children born between 1980 and 1999 received newborn hearing screening, 78 (85.7%) of the 91 children who were born between 2000 and 2013 and were enrolled in our program under one year of age had undergone newborn hearing screening at the maternity hospital. As a result of our early educational program, 13 hearing-impaired children with normal performance intelligence scores on the WPPSI Intelligence Test at six years of age (9 children with cochlear implants and 4 with hearing aids) who had been enrolled before they had reached one year of age showed average and above-average verbal intelligence scores on the WPPSI Test and were entered into regular classrooms of public primary schools at six years of age.
In conclusion, implementation of the newborn hearing screening program led to a sharp increase in the number of hearing-impaired children enrolled in the Fujimidai Auditory Center before reaching one year of age between 2000 and 2013, and enrollment under one year of age provided the hearing-impaired children with a good opportunity to achieve average and above-average VIQ scores by six years of age.